This disclosure relates to seismic surveys and seismic exploration for oil and gas. In particular, but not by way of limitation, this disclosure relates to noise attenuation of seismic surveys and noise attenuation using two dimensional (“2D”) and three dimensional (“3D”) fan filters.
Seismic exploration involves surveying subterranean geological formations for hydrocarbon deposits. A survey may involve deploying seismic source(s) and seismic sensors at predetermined locations. The sources generate seismic waves, which propagate into geological formations creating pressure changes and vibrations along the way. Changes in elastic properties of the geological formation scatter the seismic waves, changing the direction of propagation and other properties of the seismic waves. In a seismic survey, part of the energy emitted by the seismic sources reaches the seismic sensors. Some seismic sensors are sensitive to pressure changes (e.g., hydrophones), other seismic sensors are sensitive to particle motion (e.g., geophones). Seismic surveys may deploy one type of sensor or a combination both types of sensors. In response to the detected seismic events, the seismic sensors generate seismic data, generally, in the form of electrical signals. Analysis of the seismic data may indicate the presence or absence of probable locations of hydrocarbon deposits.
Some seismic surveys are known as “marine” surveys because the survey is conducted in a marine environment. However, “marine” surveys may not only be conducted in saltwater environments, they may also be conducted in fresh water and brackish water environments. In one type of marine survey, called a “towed-array” survey, an array of seismic sensor-containing streamers and sources is towed behind a survey vessel.
Other seismic surveys are known as “land” surveys because the surveys are conducted on land environments. Land surveys may use dynamite, seismic vibrators and/or the like as sources. In land surveys, arrays of seismic sensor-containing cables/seismic sensors are laid on the ground to receive seismic signals/waves generated by the seismic sources. The seismic signals may be converted, digitized, stored or transmitted by sensors to data storage and/or processing facilities nearby, e.g. a recording truck. Land surveys may also use wireless receivers to avoid the limitations of cables. Seismic surveys may be conducted in areas between land and sea, which is referred to as the “transition zone”. Other types of seismic surveys, incorporating both hydrophones and geophones, may be conducted on the seabed.
In seismic surveys, the seismic data generated by the seismic receivers may be masked by noise, such as surface related noise, e.g. strong and dispersive ground roll and scattered ground roll. One of the data processing tasks with respect to seismic data from a seismic survey is to attenuate noise in the seismic data without distorting the seismic signals.
Many methods for attenuating noise in seismic data have previously been proposed and used. For example, techniques such as wide-band velocity filtering, transformation and analysis of record sections, 3-D prestack f-x coherent noise suppression and 3-D filter design for use on a hexagonal grid are some example methods for noise attenuation.